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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Digital camera - slide scanner. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Digital technology Some time ago, the author got excited about the idea of watching slides, the number of which in his collection exceeded a thousand, on a large TV screen. The motive was that for the Etude slide projector, which had worked for many years, there were no spare lamps left, which were very short-lived. Several attempts have been made to "digitize" slides with a video camera or a conventional flatbed scanner equipped with a slide attachment. All of them were unsuccessful, the satisfactory quality of digital copies could not be achieved. It was also not possible to purchase a specialized slide scanner or scan the entire collection by contacting a specialized company due to the unreasonably high price of such devices and services. It was possible to find a solution to the problem when a Canon digital camera with a 5 Mpx matrix and the "Macro" mode was purchased. A day off was spent making the design described below, after which it was possible to transfer the entire collection of slides to digital form in just two hours. The image quality is more than satisfactory for viewing on an 81 cm TV.
And now - about the product itself, shown in the photograph of fig. 1. LED 6 with ribbed heat sink 7 is mounted on an L-shaped holder at a height of 25 mm from the base 8 - exactly on the optical axis of the camera lens 1 passing through the center of the slide fixed in the frame 4. The frame with the slide is inserted into the holder, consisting of a diffuser light 5, made of milky-colored organic glass, and two guides 3 glued to it, made of ordinary organic glass 4 mm thick. Between the guides, you can install any frames of standard sizes 50x50 mm. Two springs 9 made of steel wire press the frame against the diffuser. Close to the rails on the side of the frame, two narrow strips of organic glass 1 mm thick are glued onto the diffuser. They do not fall into the slide area and help not to scratch the diffuser when changing the frame. The radiation angle of the super-bright white LED EP505L-350W1 used to illuminate the slide is 120 degrees. Being mounted at a distance of 40 mm from the diffuser, this LED illuminates the entire surface of the slide quite brightly and evenly. The camera is rigidly fixed on plate 11 2,6 mm thick. By releasing the screws 10, it can be moved together with the plate, ensuring that the slide image occupies as much of the frame area as possible with optimal focus. Having found this position, the screws 10 should be tightened. If, after assembling the installation, it turned out that the optical axis of the lens passes above or below the center of the slide and the LED, the thickness of the plate 11 will have to be changed accordingly. The camera shutter button can be pressed manually. But if you connect the machine to the computer's USB bus, then if you have the appropriate program, you can control shooting from the computer keyboard. This will significantly reduce the risk of spoiling the frame due to accidental slide shift when pressing the button too hard. Experience has shown that the light reflected by the shiny end surface of the lens barrel, falling on the slide, often creates glare in the image. To avoid this, aperture 2 of an opaque material was installed between the lens and the slide. The diameter of the aperture opening is equal to the diameter of the glass lens of the objective. To eliminate glare, the entire structure (with the exception of the slide holder) is painted black.
The LED power supply is made according to the scheme shown in fig. 2. LED HL1, used as a stabistor, sets the voltage based on the transistor VT1. By changing the total resistance of the resistors in the emitter circuit of this transistor, its collector current is regulated, and, consequently, the current flowing through the EL1 LED. When working with color slides, the SA2 switch is closed, while a current of about 1 mA flows through the EL150 LED, the voltage drop across the LED at this current is approximately 3,5 V. For black and white slides, the illumination is often excessive, so the SA2 switch is opened and the current reduce the variable resistor R4, controlling it on the device RA1. When setting up the installation by selecting a resistor R1, it is ensured that the current of the total deflection of the arrow of the device RA1 becomes equal to 200 mA. Transformer T1 can be used with any winding voltage II indicated in the diagram and an overall power of more than 5 V-A. The KTs402A diode bridge can be replaced by another one with a current of more than 0,5 A and a voltage of at least 100 V. Author: A. Stepanov, St. Petersburg; Publication: radioradar.net
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